Three-wire electric system



(N0 Model. V.

E. M. HEWLETT & W. B. POTTER THREE WIRE ELEGTRIU SYSTEM.

No. 554,270. Patented Feb. 11, 1896 WI TNESSES NAM. PNOTBLUHQWASNINGTONDC UNITED STATES PATENT OFFICE.

ED\VARD M. HETVLETT AND YVILLIAM B. POT"ER, OF SCIIENEOTADY, NElV YORK,ASSIGNORS TO THE GENERAL ELECTRIC COMPANY, OF

NEYV YORK.

TH REE-WIRE ELECTRIC SYSTEM.

SPECIFICATION forming part of Letters Patent No. 554,270, dated February11, 1896.

Application filed September 10, 1895. Serial No- 562,046. (No model.)

To all whom it may concern.-

Be it known that we, EDWARD M. HEW- LETT and WILLIAM B. POTTER, citizensof the United States, residing at Schenectady, in the county ofSchenectady and State of New York, have invented certain new and usefulImprovements in Threeire Electric Systems, of which the following is aspecification.

The object of the present invention is to allow a compound -woundgenerator to be thrown onto either side of a three-wire system forpower, electric lighting, or railway work.

Heretofore three-wire systems have been supplied by shunt-woundgenerators, and all that is necessary in this case, when throwing amachine from one side to the other, is to reverse the mains leading fromthe generator to the bus-bars on the switchboard, and if the current andpotential indicating instruments are between the generator and thebusbars the connections to them would have to be reversed. Such a systemwas described in patent to E. M. Hewlett, No. 537,533, dated April 16,1895.

I11 running compound machines, as ordinarily connected, there is anequalizing connection between the positive brushes of the severalmachines which equalizes the flow of current through the series coil ofeach generator. It is evident that this coil must energize the field inthe same direction as the shunt-winding, and if the main leads weresimply reversed the current flowing through the equalizer from the othermachines would be opposed to that generated by the reversed machine, soin order to have the current fiow through the series coil in the rightdirection two equalizers are provided, one for the machines on thepositive sides of the system and the other for those on the negative,and we style these positive and negative equalizers. There is always acertain amount of magnetism in a field-pole, even when there is nocurrent flowing in the energizing-coils, and to insure the machinegenerating current in the proper direction a current is momentarilypassed through the fields from the bus-bars, and in such a directionthat when the generator starts up the currentwill be of the same sign asthe side on which it is thrown. This method of insuring themagnetization of the proper sign is commonly known as flashing.

The invention further consists in arranging two of the switches with aninterlocking mechanism between them, so that when the machine is beingflashed the switch closing the field-circuit onto the machine cannot bethrown. To indicate when the current is passing through the field due tothis cause, we place a number of incandescent lamps in circuit in such amanner that the throwing of the switch will cause them to light.

In the accompanying drawing there is shown diagrammatically a stationwith a machine connected to either side of the system, and a sparemachine adapted to be thrown on either side.

Although only one machine is shown as being provided with switches forchanging the circuits, it is evident that any or all of the machinescould be so provided.

A, B, and 0 represent, respectively, the positive, neutral, and negativebus-bars of a three-wire system.

D is a positive equalizer and E is the nega tive.

For the purpose of illustration one machine is shown as beingpermanently connected to each equalizer, but it is understood that in acentral station there would be several such machines.

hf is a compound-wound generator with a resistance L for regulating thefield, and is shown as feeding the positive side of the system while themachine 1' is feeding the negative. Machine M is open-circuited, butthere is current flowing through the field-windings from the positivebus-bar A through the lefthand side of the switch F, through the seriesand shunt windings, resistance L, switch H to the neutral bus-bar B.There would also be a current passing from a point through the lamps Kto the switch I, to the switch H where it would unite with the currentfrom the fieldwindings. The connections through the switch F wouldequalize any difference of potential between the machines on theopposite side of the system.

If the switch 11 were thrown down, so as to close the circuit on thecontacts ff, the current would pass thrmigh the field-windings and lampsas before, but it would be of the opposite sign, 'f'or they areconnected with the negative side ot the system.

lfieeders O O are connected to the positive side of. the system and. N Nto the negative. In order to prevent the switch I from being closed.while switch it is closed, an arm .l is connected to the lower part of.the switch I in such a manner that the end strikes against the blade of?switch ll. and prevents further movement tliereot until ll has beenopened. ()n the otherhand, it"switchl is closed II cannot be thrown, forthe arm .l projects under the blade, preventing it from closing.

Assume, for example, that the positive side of the system is overloadedand that it is necessary to throw the spare machine It onto that side.If; this machine has previously been used on the negative side of thesystem the residual magnetism would tend to build the machine up in thesame direction as before. As this would make the electromotive force ofthis machine oppose the others on the same side of the system it; isnecessary to insure the magnetization in the proper direction, and thisis done by opening the circuit of the machine at the switch G andclosing switches 11 and ii, as shown, which will allow a current fromthe bus-bars to How through the tields in such a direction as to insurethe magnetization of the fields being in the proper direction. todeliver a positive current from the right-hand brush when the machine isstarted up. It is only necessary to close this circuit momentarily,after which the switch ll .is opened andv switch I closed, thus throwingthe shunt-field onto its own armature. After the machine has come up tospeed in the usual way the switch G is closed, com pleting the circuitto the positive side of the system.

If it were desired to throw the machine M onto the negative side of thesystem, the same procedure would be followed, except that the switch Fwould be thrown down, and then the machine would build up with anegative potential. at the right-hrmd brush and the currcnt flowingthrough the series coil would be equalized by the negative equalizer E.

hat we claim as new, and desire to secure by Letters Patent of. theUnited States, is

1. The method of changing a compoundwound generator from the positive tothe negative side of a three-wire system or vice versa which consists ininterrupting the main circuit, flashing the fields :t'rom the side ofthe system on which the machine is to be thrown, closing the shunt-fieldupon its own armature, and .tinally closing the main switch of thegenerator, thus completing the circuit.

2. In a three-wire system the combination of e01npouml-wotmd generatorsconnected to bus-bars, positive and negative equalizers, and switchesfor reversing the connections of the series coils when changed .t'romthe positive to the negative side of. the system or vice versa.

'3. In a three wire system, the combination of compound-weund generatorsconnected respectively to the positive and negative sides ot the system,positive and negative equal- .izers, equalizing the flow oi current ontheir respective sides of the system and switches for throwing themachines from one side to the other.

1-. In a three-wire system, the combination of compound-weund generatorssupplyi ng the sides of the system, with positive and negativeequalizers eq nalizing the current: on their respective sides, andswitches for changing the connections of the machines from one side ofthe system to the other.

The C(HllblilttilOll, with a three-wire system, of a compotunl-wouiidgenerator provided with a switch or switches [or changing the connectionof the series coil from the positive to the negat ive equalizer or viceversa when the machine is changed from one side oi? the system to theother.

(3. The combination, with a three-wire tem, of a compound-woundgenerator adapted to be thrown on either side thereof, and a switch orswitches for closing the fields on a local circuit between one side ofthe system and the neutral to give them an initial magnetization in theproper direction.

7. In. combination with a three-wire system, a compound-wound generatoradapted to be thrown on either side of the system, a switch for closingthe fields on a circuit from the bus-bars, a switch for closing theshunttield upon the armature ot' the machine, and an interlocking devicebetween the switches whereby only onecan be thrown at a time.

S. The combination, in a three-wire system, of a compo and-wound generator adapt ed to be thrown upon either side of the system, switches forreversing the connections oi. the series coil and equalizer, a switch[or closing the fields on a local circuit with the bus-bars, and atwo-way switch for completing a lampcircuit in one position and theshunt-field circuit inv the other.

9. The combination, in a three-wire tem, of a compound'wound genertttorprw vided with switches for reversin the connections when changed :tromone side of.' the system to the other, means for giving the fields aninitial magnetization in the proper direction, indicating-lamps incircuit with said means, and a switch for cutting out these lamps whenthe fields are closed upon the machine itself.

In witness whereof. we have hereunto set our hands this 0th day ofSeptember, 1893.

ETNVARD M. lilClVLlllil. \VILTJIAM Ill. lO'lTlClt.

"\t'itnesses:

A. F. MACDONALD, F. E. CASE.

TIO

